A fuel cell refers to a device that electrochemically generates electricity using hydrogen gas and oxygen gas. More specifically, the fuel cell converts hydrogen and air, which are continuously supplied from outside, into electrical energy and thermal energy through an electrochemical reaction.
Such a fuel cell generates power using an oxidation reaction in an anode and a reduction reaction in a cathode. At this time, a membrane electrode assembly (MEA) including a catalyst layer and a polymer electrolyte membrane is used in order to promote oxidation and reduction reactions, the catalyst layer including platinum or a platinum-ruthenium alloy. A conductive separator is coupled to both ends of the MEA so as to form a cell structure.
Since a unit cell of the fuel cell has a low voltage, the practical utility thereof is inevitably low. Thus, several or several hundred unit cells are generally stacked and used. When unit cells are stacked, a metal separation plate serves to electrically connect the respective unit cells and separate a reaction gas.
A general metal separation plate for a fuel cell includes a reaction gas channel and a cooling water channel, which are formed in the center of a rectangular metal plate, and a gasket surrounding the reaction gas channel and the cooling water channel. The reaction gas channel and the cooling water channel may be collectively referred to as a channel part. Typically, the reaction gas channel is formed through a stamping process which is performed from the front surface to the rear surface of the metal plate, and the cooling water channel is formed by utilizing an area between the reaction gas channels protruding from the rear surface of the metal plate. According to the structure of the channel part, a reaction gas may flow on the front surface of the metal plate, and cooling water may flow on the rear surface of the metal plate. For this reason, the front surface of the metal plate may be referred to as a reaction gas flowing surface, and the rear surface of the metal plate may be referred to as a cooling water flowing surface.
The metal separation plate has a water-cooled structure in which cooling water introduced into a cooling water introduction manifold at one side of the channel part cools heat while passing through the cooling water channel, the heat being generated by an activation loss, reduction reaction in the anode, and Joule heating, during operation of the fuel cell. The cooling water having passed through the cooling process is discharged to the outside of the metal separation plate through a cooling water discharge manifold at the other side of the channel part.
In the case of the water-cooled metal separation plate, cooling water must be continuously supplied to the metal separation plate in order to cool the heat generated during the operation of the fuel cell. In this case, the water-cooled metal separation plate requires a pump for supplying cooling water, a deionizer, a heat exchanger and the like, thereby increasing the manufacturing cost of a fuel cell system. On the other hand, an air-cooled metal separation plate has an effect of reducing the manufacturing cost of a fuel cell system.
However, the air-cooled metal separation plate has a total of two cathode layers which include a cathode separation plate for supplying air and a cooling plate for securing a space in the vertical direction to smoothly supply air, the cooling plate serving as a cooling fin. In this case, since the cooling plate is additionally required, the entire volume and manufacturing cost of a fuel cell stack are inevitably increased.
The related art of the present invention is disclosed in Korean Patent Laid-open Publication No. 10-2003-0042633 published on Jun. 2, 2003, and provides a fuel cell stack which includes a cooling plate having an air-cooled structure and stacked between unit cells.